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Just about everyone has heard of the “black box” on an airplane. The term tends to have strong associations because most of the time when we hear about the black box it’s as a result of an air crash. Here’s a look at how they work.
“Black box” is a common term in popular use but within the industry it is generally referred to as an electronic flight data recorder. That can describe either the CVR (Cockpit Voice Recorder) or the FDR (Flight Data Recorder), or a combination of both. A number of modern black boxes house everything within one unit. Either way, for redundancy’s sake, every aircraft has to have at least two onboard. And they do exactly what they say on the tin: these boxes are essentially heavily fortified hard drives that record everything about a flight on an ongoing basis.
The FDR continuously records a wide array of data (around 700 different parameters) about all aspects of an aircraft as it flies from place to place. The CVR records the conversations on the flight deck and other sounds like radio transmissions and automated alarms, though it deletes all audio older than the most recent two hours of flight. //
Although the hope is always that the data any given black box contains will never need to be retrieved and analyzed, every recorder needs to be able to withstand the worst case scenario: a catastrophic accident. That means they need to be certified as more or less indestructible, at least up to some very high thresholds. They’re tested by being launched at a concrete wall at a speed of 750 kilometers per hour, and they have to withstand loads of 2.25 tons for at least five minutes, temperatures of 1,100 degrees Celsius for an hour and not only be waterproof but withstand the heavy pressure found at depths of thousands of meters underwater. //
Consider the fact that after the crash of Air France flight 447 in the Atlantic Ocean in 2009, the black boxes weren’t found until nearly two years later. The wreckage that contained the boxes was submerged at a depth of almost 4,000 meters. And yet, the data and recordings were successfully recovered and proved invaluable for helping investigators to understand exactly what went wrong.